Best Way to Test for Cyclospora Infection

 Routine ova and parasite (O&P) testing is likely to miss a Cyclospora infection, so physicians should be sure to request additional methods when searching for a diagnosis, testing experts said.

"The thing physicians may not know is if you order a test for O&P, you're not going to get it," Thomas A. Moore, MD, an infectious diseases physician at the University of Kansas School of Medicine–Wichita, told MedPage Today. "You have to specifically ask for Cyclospora" via staining that isn't routinely done, he said.

The modified acid-fast stain can sufficiently detect the parasite by dyeing it an easily identifiable color in a stool sample under the microscope, experts said.

There's also ultraviolet fluorescence microscopy, which makes the parasite "glow" in a way that chemical staining might miss. This, however, is not used as commonly, they noted.

Looking for the parasite's DNA is another option, usually via multiplex gastrointestinal polymerase chain reaction (GI-PCR). Moore likes the multiplex panel because it's a "catchall."

"So, if it happens to be Cyclospora, great, but if it's not, you know what else it is," as patients can be infected with other organisms, he noted.

Still, Moore emphasized that "you have to tell the lab, wherever you send it, that you suspect Cyclospora" because not all multiplex panels include this parasite.

Joel Barratt, PhD, a molecular parasitologist at Emory University School of Medicine in Atlanta, pointed out that DNA tests are "far more expensive" than microscopy, but also more sensitive. (Physicians on social media have reported out-of-pocket costs of up to $1,000 for DNA testing.)

When there are very few parasites in a sample, they may not be immediately obvious under a microscope -- but their DNA can still be detected, Barratt said.

"If cost is not a consideration, then PCR-based tests are more likely to detect a true Cyclospora infection than microscopy," he said. But "if you are worried about cost, microscopy-based tests are cheaper and will detect a Cyclospora infection most of the time, if one is present."

Also, if microscopy returns a negative test, and Cyclospora is still strongly suspected -- for example, if the patient ate produce known to carry the parasite, such as iceberg lettuce -- a multiplex GI-PCR panel can confirm whether the negative microscopy result is a true negative, Barratt added.

False positives are not common, Christopher Attaway, MD, a pathologist at the University of Vermont's Larner College of Medicine in Burlington, told MedPage Today. There is greater concern that cases might be missed because the parasite may not shed consistently. Testing multiple stool samples can increase the likelihood of detection, he added.

He noted that "in the real world, only the modified acid-fast stain of stool specimens and the multiplex GI-PCR panel are readily available," while UV fluorescence is "uncommon." He personally does not know any labs that offer it.

Attaway would recommend the multiplex GI-PCR panel for immunocompromised patients, but for otherwise healthy patients, the modified acid-stain is "perfectly fine."

And if clinical suspicion is high, both Moore and Attaway said it's reasonable to start treatment before tests confirm a case.

https://www.medpagetoday.com/infectiousdisease/publichealth/122242